0:00 In this video we're going to continue on from the bacteria, the structure, and 0:18 look at the 0:19 growth, reproduction, and classification, partly. 0:22 Now, an important thing to know before looking at the growth of a bacteria is 0:28 that we have 0:29 to understand that a bacteria is a prokaryote, all bacteria are prokaryote, 0:34 meaning that they 0:35 are single-celled organisms. Humans, such as ourselves, have multiple cells 0:41 making up us one 0:42 organism. Bacteria has only one cell making up that organism. So, the growth of 0:50 a bacteria is defined 0:51 in terms of an increase in cell number rather than cell size. And how the 0:59 bacteria replicate 1:02 is not through mitosis and meiosis, but through a process known as binary 1:07 fusion. So, bacteria 1:09 reproduce by binary fusion. So, here we have a simple bacteria with the DNA 1:15 inside circular DNA, 1:17 might I say, nucleomara. Next, the DNA will be replicated during binary fusion, 1:23 replicated like 1:24 so, and then the DNA will divide, and what's called a transverse septum will be 1:29 formed by the cell 1:30 wall and the membrane. So, sort of like it didn't. So, here we have the trans 1:36 verse septum. And then, 1:38 after some time, a transverse septum will be completely formed, which will 1:42 enable the daughter 1:44 cells, these two cells, to separate now. So, now we have two bacteria cells. 1:49 And that completes 1:50 binary fusion, how the bacteria reproduces itself. Now, the time taken for a 1:56 cell, the bacteria, 1:57 to reproduce itself is called a generation time, and this can vary depending on 2:03 the type of organism 2:05 and the environment conditions. So, under favorable conditions, for example, 2:09 the bacteria can reproduce 2:13 a lot. Under bad conditions, they won't reproduce at all. You can calculate the 2:19 generation time 2:21 by doing simple mathematics, so where generation time is equal to time taken, 2:27 divided by the number 2:29 of generations. But we won't really look into that now. What we will look into 2:35 now, however, 2:37 is the growth of a bacteria. And we can investigate the growth of bacteria by 2:43 putting, 2:43 by isolating a bacteria and putting it inside a medium, such as a petri dish, 2:47 which makes the 2:48 bacteria in culture now. And under certain laboratory conditions, we can view 2:54 the growth phases of a 2:55 bacteria. Bacteria has four growth phases, and we can view this on a graph. The 3:02 x-axis of this graph 3:04 is increasing time, and the y-axis is the logarithmic number of cells. 3:09 So, this, now we are looking at the four phases of growth for a bacteria. The 3:16 first phase is known 3:18 as a lag phase, and cells, and in this phase, the bacteria need to adapt to the 3:23 new medium, 3:24 because it was just placed there. After some time, we have the log phase, 3:30 while cells are an optimum growth state, and perform birefusion, reproduction 3:36 process. 3:37 And as you can see, during the log phase, there is a logarithmic increase in 3:42 cell number. 3:43 So, what this means is that we start off with one bacteria. When it performs b 3:51 irefusion, we have two, 3:53 and then a birefusion again, we have two to the power of two. We have four, and 3:58 then this process 3:59 will continue, two to the power of three, and then two to the power of four. 4:02 And this process, where the bacteria keeps dividing in a linear sort of fashion 4:08 , is known as a 4:09 logarithmic increase in growth, or an exponential increase. And so, this is the 4:14 log phase. 4:15 Now, after the log phase, we have the third phase, which is a stationary phase, 4:20 and this is, 4:21 and as you can see, it just goes flat. The logarithmic number of cells just 4:27 becomes flat, 4:27 it doesn't increase. And this is due to the exhaustion of some critical new 4:31 nutrition, or 4:33 the accumulation of waste product, which basically essentially slows the growth 4:39 , or stops the growth 4:41 of the bacteria in the culture. And then, after the stationary phase, we have 4:45 the death or decline 4:47 phase. And this is, this essentially occurs through the continuation or 4:52 accumulation of waste 4:53 products, or exposure to oxygen, perhaps. And in this phase, you can see that 4:57 the number of bacteria 4:59 decreases. I hope that made sense. The graph I just drew essentially showed us 5:04 the four phases 5:05 of bacterial growth. But of course, the growth of the bacteria had to be under 5:12 a good condition, 5:13 under laboratory conditions. So essentially, there are requirements for a 5:18 bacterial growth. 5:21 And there are many factors which influence bacteria growth. The fact, the main 5:25 factors affecting 5:26 growth that we will look at now are temperature, pH, wastewater, sorry, and osm 5:33 otic pressure, and 5:34 also oxygen. There is also nutritional requirements, which we will not look 5:40 into in this video. 5:42 Before we continue on with the requirements for bacterial growth, we have to 5:46 understand that 5:47 each bacteria is unique, in that they require different, different temperatures 5:52 , different pH, 5:53 different oxygen concentrations for growth. And let's begin by looking at 5:58 temperature first, 6:00 first, and see how it affects bacterial growth. By looking at a graph, here we 6:05 have a graph, 6:06 the y-axis represents the rate of growth. So the rate of bacteria grows. And 6:13 remember, 6:14 the growth of bacteria is not an increase in size, but an increase in number. 6:19 And the x-axis is the 6:21 temperature from negative 10 degrees Celsius to 80 degrees, which is near 6:26 boiling point, right? 6:27 So this first graph, where we see an increase in rate of growth, are a group of 6:34 bacteria known as 6:35 psychrophiles, and they are essentially cold blooded, actually cold loving 6:40 rather. And their optimum 6:42 growth is about 10 degrees Celsius, so really cold. And we can see the 10 6:47 degrees Celsius that 6:48 we have optimum growth for these types of bacteria. The other type of bacteria 6:52 are known as mesophiles, 6:54 and their growth are optimum at about between 25 to 35 degrees Celsius. And as 7:01 you can see by the 7:02 graph, the top is roughly around this area. And then we have bacteria known as 7:07 thermophiles, 7:08 which grow mostly under hotter conditions, where the optimum is about 60 7:15 degrees Celsius. And after 7:18 this, we can even have other extreme thermophiles, which have optimum growth 7:24 over 80 degrees Celsius, 7:26 nearly 100. So from this graph of temperature, we can see how there are 7:31 different bacteria 7:34 required different temperatures for optimum growth. Next, let's look at pH. pH 7:40 also is a 7:41 important factor affecting bacterial growth. pH, if you know, goes from 0 to 14 7:47 , where 0 is, 7:48 well, towards 0 is more acidic, towards 14 is more basic. Different bacteria 7:55 require different 7:56 pH in order to grow optimally. If they are grown in a pH that is not suitable 8:03 for them, they will 8:03 die, essentially. Bacteria which grow best in pH between 0 and 6, which is more 8:12 to acidic side, 8:15 are known as acidophiles, meaning they love acids. Bacteria which grows optim 8:20 ally between a pH of 8:21 6 and 9, let's just say, are called neutrophils, because they're neutral. And 7 8:25 is a neutral pH. 8:26 Then we have bacteria which grows optimally under basic conditions, so pH of 10 8:32 and over. 8:33 They are known as alkylophiles. Another factor which affects bacteria, the 8:43 growth of a bacteria, 8:45 is the water and osmotic pressure. Bacteria grow best in areas saturated with 8:52 water. 8:53 The increase in pressure in a bacteria causes the cell to burst as well. And so 9:03 an optimum 9:04 pressure is required. Oxygen is another factor which greatly influences 9:11 bacterial growth, 9:13 because bacteria can be either anaerobic or aerobic or in between. So let's 9:20 look at some 9:20 classifications of bacteria with oxygen. First of all we have what's called 9:27 obligate aerobes, 9:28 which means these are the types of bacteria which requires oxygen in order to 9:32 survive. 9:33 Then we have facultative anaerobes, which grow with or without oxygen, but they 9:39 grow better with 9:40 oxygen. Then we have aero-tolerant anaerobes, which are bacteria which grow 9:46 equally well with 9:47 or without oxygen. Obligate anaerobes are bacteria cells which die in the 9:53 presence of oxygen. 9:54 And then we have these special cases of bacteria, such as microaerophiles, 9:58 which are bacteria cells, 10:00 which won't grow at normal atmospheric oxygen levels, which is 20%, because, so 10:06 for example, 10:07 they won't grow in the room you are sitting in now. But these bacteria only 10:12 require some 10:13 oxygen for growth between 2 and 10%. Then we have capenophiles, which are 10:18 bacteria which 10:19 require carbon dioxide. So from all these factors which affect bacterial growth 10:24 , I hope you can 10:25 begin to appreciate all these factors which can affect bacterial growth. I hope 10:31 this video was 10:32 okay. Hope you enjoyed and made sense. It might be confusing between generation 10:36 time and growth 10:37 phases. You can read up on that if that's still confusing. Thank you.
